Experimental evaluation of the viscoelasticity of porcine vitreous

Abstract

This study aims to estimate the material properties of the porcine vitreous while testing it in close to its natural physiological conditions. Eighteen porcine eyes were tested within 48 h post-mortem. A custom-built computer-controlled test rig was designed to support, load and monitor the behaviour of eye globes while being subjected to dynamic rotation cycles mimicking saccade eye movement. Specimens were glued to the base of a container, surrounded by gelatin, frozen and cut in half to expose the vitreous. After thawing, the container was subjected to concentric dynamic rotations of up to 5°, 10° or 15°, while taking 50 MP photos of the specimen every 2 ms. The images were analysed by a digital image correlation algorithm to trace the movement of marked points on the vitreous surface with different radii from the centre of the posterior chamber. The initial camera image was used in building a finite-element model of the test set-up, which was used in an inverse analysis exercise to estimate the material properties of the vitreous. Angular displacements of the monitored points were up to 3.3°, 4.1° and 3.9° in response to eye rotations of 5°, 10° and 15°, respectively. With the experimental relationships between eye rotation and angular displacements used as target behaviour, the inverse analysis exercise estimated the initial shear modulus, the long-term shear modulus and the viscoelastic decay constant of the porcine vitreous as 2.10 ± 0.15 Pa, 0.50 ± 0.04 Pa and 1.20 ± 0.09 s −1 , respectively. Consideration of the viscoelasticity of the vitreous was essential to represent its experimental behaviour. Testing the vitreous in close to its normal physiological conditions produced estimations of the initial shear modulus and long-term shear modulus that were, respectively, smaller and larger than reported values (Zimberlin et al . 2010 Soft Matter 6, 3632–3635. ( doi:10.1039/b925407b ), Liu et al . 2013 J. Biomech. 46, 1321–7. ( doi:10.1016/j.jbiomech.2013.02.006) , Rossi et al . 2011 Invest. Ophthalmol. Vis. Sci. 52, 3994–4002. ( doi:10.1167/iovs.10-6477 )).

Assessment of age-related change of the ocular support system

“…With this information, numerical modelling of the eye globe, especially those simulating WEM, can now include models of the OST rather than introducing non-physiologic boundary conditions simulating its effect. Aboulatta et al (2021) ; Jannesari et al (2018) Nevertheless, despite consideration of the orbital geometry’s irregularity, numerical simulations did not accurately represent the nasal rotation aspect of clinical retraction of the eye globe. The authors of this study suggest that this rotation may be due to deeper orbital structures, such as EOMs, Lockwood’s ligament or other connective tissues.…”

“…For quite some time, numerical modelling of the OST did not get much attention. Despite the essential findings achieved by previous ocular modelling studies ( Stitzel, 2002 ; Elsheikh et al, 2013 ; Aboulatta et al, 2021 ), the effect of the OST was ignored, and the ocular globe was provided with boundary conditions that were assumed to represent the restraints provided by the OST. These boundary conditions commonly restrained the eye’s equatorial zone against the movement in the longitudinal direction while permitting it to expand or move laterally ( Elsheikh et al, 2013 ).…”

An Inverse Method to Determine Mechanical Parameters of Porcine Vitreous Bodies Based on the Indentation Test

“…In addition to rheometers, the mechanical testing machine was also used to determine the elastic module of the vitreous body using compression tests while it was put on a 35 mm diameter Petri dish [ 14 ]. However, all these vitreous body specimens were removed from the eyeball, which may lead to changes in the mechanical properties [ 22 , 23 ].…”

“…FEM is a numerical method used to solve the differential equations and has been widely used to analyze the mechanical response of complex organisms under the action of forces [ 44 , 45 , 46 , 47 , 48 , 49 , 50 , 51 ]. The mechanical parameters of the porcine vitreous body were estimated by combining the experimental results and finite element method [ 22 ].…”

Combined electromechanically driven pulsating flow of nonlinear viscoelastic fluids in narrow confinements

“…Motion of viscoelastic fluids in narrow confinements has recently emerged as a realm of great interest owing to its applications in cutting edge areas such as polymer processing [1,2], food processing [3], manipulation of biofluids related to medical applications [4][5][6][7][8], to underline a few. The reason may be attributed to the ability of these non-Newtonian fluids to mimic the rheological behaviours of various bio-relevant media such as blood [9,10], synovial fluids [11,12], human saliva [13][14][15], which in many cases are analysed under micro-or, millifluidic environments [10,16,17].…”